The objectives of this proposal are the synthesis and evaluation of novel selective inhibitors of steroid-transforming enzymes. Some of these steroid analogs are designed as active site-directed irreversible inhibitors of delta5-3-ketosteroid isomerase, and others are designed as inhibitors of 3 beta- and (3 and 17)beta-hydroxysteroid dehydrogenases and of processes involved in the oxidative degradation of lanosterol and of cholesterol. Others are intended to be reversible inhibitors of these enzymes. The mechanisms by which enzyme inhibition occurs will be studied.